1. Field of the Invention
The present invention relates to an image display apparatus for displaying images such as television images.
2. Description of Related Art
In recent years, image display apparatuses for displaying images, such as television images, have become thinner. Accordingly, for the image display apparatuses, flat panel displays (hereinafter referred to as FPDs) using a flat-type display panel, such as a plasma display panel (hereinafter referred to as a PDP) and a liquid crystal panel, have become a mainstream instead of the CRTs (cathode-ray tubes) of the past.
For example, since the plasma displays using the PDP display images by utilizing the gas discharge caused in the PDP, they have the characteristics that the PDP tends to have a high temperature easily during operation. The high temperature of the PDP changes the electric capacity of the electrode formed in the PDP, causing adverse effects such as normal discharge not being performed. Thus, in the case of using a plasma display, it is necessary to radiate heat generated in the PDP and maintain the interior of the PDP within a predetermined temperature range.
Conventionally, various types of radiation structures have been proposed in order to radiate the heat generated in the display panel such as the PDP. Generally, PDPs employ an air-cooling-type radiation structure in which a cooling fan allows air to flow between the PDP and a chassis so as to lower the PDP temperature (see JP 2000-040474 A, for example).
However, in the air-cooling-type radiation structure as mentioned above, the heat transfer from the display panel to air is insufficient, and it is likely to be impossible to deal with the amount of heat increasing due to the further reduced thickness and increased luminance of the FPD.
Also, the amount of heat generated during operation tends to increase rapidly in electronic apparatuses, such as portable computers, due to their higher processing speed and multi-functionalization. As a result, the air-cooling-type cooling system using a conventional motor-driven fan cannot deal with such heat any more, and it is proposed to use a liquid-cooling-type cooling system using a cooling liquid having a specific heat higher than that of air. For example, JP 2003-324174 A discloses a structure in which a liquid-cooling-type cooling unit radiates the heat generated in a high-heat-generating component (central processing unit) of an electronic apparatus.
With reference to FIG. 8, an example of electronic apparatuses with the radiation structure utilizing the liquid-cooling-type cooling system will be described.
A portable computer 101, which is an example of the electronic apparatuses, is constituted by a main body 102 and a display unit 103. The portable computer 101 includes a liquid-cooling-type cooling unit for cooling a semiconductor package 104 that is a high-heat-generating component. The cooling unit includes a heat-receiving head 105 serving as a heat receiving portion disposed in the main body 102, a radiator 106 serving as a radiating portion disposed in the display unit 103, and a circulation passage 108 for allowing a cooling liquid to circulate between a refrigerant passage (not shown) of the heat-receiving head 105 and a refrigerant passage 107 of the radiator 106. The heat generated in the semiconductor package 104 is absorbed by the cooling liquid in the refrigerant passage of the heat-receiving head 105. The cooling liquid that flows through the heat-receiving head 105 and has absorbed the heat is pumped into the radiator 106 disposed on a display unit 103 side by using a centrifugal pump 109. The refrigerant passage 107 of the radiator 106 is disposed so as to follow a meandering path between a rear surface of a display panel (not shown) and a housing 110. The cooling liquid is cooled by the heat exchange occurring when it passes through the radiator 106. The cooling liquid cooled in the radiator 106 is returned to the refrigerant passage of the heat-receiving head 105 via the circulation passage 108. Repetition of this cycle allows the heat generated on a main body 102 side to be radiated to the display unit 103 side.
In addition, as an example of the FPD utilizing the liquid-cooling-type cooling unit, there has been proposed a radiation structure in which a cooling layer into which the cooling liquid has been poured is provided on a rear surface of a liquid crystal display panel, and heat radiating fins disposed so as to surround the cooling layer radiate the heat that the cooling layer has received (see JP 2(1990)-153317 A).
There also has been proposed a radiation structure in which an airtight casing formed between a display surface of a PDP and a front panel is provided on a display surface side of the PDP, and the cooling liquid filling the airtight casing cools the heat generated in the PDP (see JP 5(1993)-121005 A). This structure includes a convection tube connecting an upper portion and a lower portion of the airtight casing via a rear surface of the PDP. A heat sink is formed somewhere in the convection tube. The heat generated in the PDP is transferred to the cooling liquid contained in the airtight casing, and then is transferred from the convection tube to the heat sink by convection so as to be radiated outside.
However, in the radiation structure proposed in JP 2003-324174 A as a cooling system for electronic apparatuses, the heat is radiated by allowing the cooling liquid that has received the heat generated on the main body 102 side to pass through the refrigerant passage 107 disposed between the rear surface of the display panel and the housing 110 (see FIG. 8). Thus, applying this radiation structure to an image display apparatus, such as a plasma display, requires a flow passage for achieving sufficient heat radiation to be provided in a rear surface region of the display device of the image display apparatus. This thickens the image display apparatus and makes it difficult to reduce the thickness of the apparatus.
Furthermore, in accordance with the thickness reduction to be accelerated further in the future, a gap between the display device of the image display apparatus and the rear housing is reduced, and the temperature of the housing behind the display device rises. This makes it difficult to utilize the rear surface region of the display device as a heat radiating portion.
In the radiation structure disclosed in JP 2(1990)-153317 A, a space to be filled with the cooling liquid is needed in a thickness direction all over the panel, increasing the thickness of the unit. Moreover, since the cooling liquid is circulated by natural convection, reducing the thickness of this portion makes it difficult for the cooling liquid to circulate, lowering the efficiency in radiating heat. As a result, thickness reduction using this radiation structure is difficult. Also in the radiation structure disclosed in JP 5(1993)-121005 A, a space to be filled with the cooling liquid is needed in a thickness direction all over the panel, increasing the thickness of the unit. Since this radiation structure requires the space to be large enough to allow the cooling liquid to circulate, it is difficult to make this portion extremely thin. Accordingly, thickness reduction using this radiation structure is difficult. As a result, it is likely to be difficult to apply these structures to image display apparatuses that generate an increasing amount of heat and are required to be further thinner in the future.
As mentioned above, there conventionally have been no effective means for applying the liquid-cooling-type cooling system to image display apparatuses, and it has been difficult to deal with the amount of heat increasing due to the further reduced thickness and increased luminance.